1. Field of the Invention
This invention relates to a method of making a magnetic core having a significantly low core loss, and more particularly, it pertains to a method for using oriented silicon iron alloy particles which when insulated, compacted and annealed provide a magnetic core exhibiting a very low core loss.
2. Description of the Prior Art
The term "microlamination" which has been defined in U.S. Pat. Nos. 3,848,331 and 3,948,690, and in general terms relates to a small rectangular particle of low carbon steel, when processed in a specific manner, is capable of being formed into a magnetic core or compact possessing soft magnetic characteristics which are useful in a myriad of applications, for example a light ballast, and as shown in U.S. Pat. No. 3,235,675. A typical low carbon steel comprises about 0.10% C, less than 0.04% S, less than 0.60% Mn, and about 0.10% Si; i.e., a grade of steel that is known as AISI Type 1010 steel in the trade. Generally, the processing of microlaminations include a decarburization, deoxidation, and stress relief anneal, the application of an insulating medium, and compaction of the microlaminations to a usable magetizable compact form. The method of compaction is either uniaxial or isostatic in nature. The resultant compact exhibits a core loss of nominally 5.25 to 7 watts per pound at an induction of 14 kG. When the compact is subsequently annealed to relieve stresses resulting from the prior compaction step, the core loss increases dramatically by a factor of from 2 to 10. For example, a ring core pressed at 125,000 psi from 0.060.times.0.010.times.0.006 inch particles of low carbon steel has a core loss of approximately 6.6 W/lb at 14 kG. After a 10 minute stress relief anneal at 700.degree. C. in dry hydrogen, the core loss is increased to approximately 33.2 W/lb at 14 kG. Manifestly, the impairment of the loss characteristics is intolerable.